Messages in this thread | | | Date | Mon, 07 Jul 2014 18:10:20 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH v2 1/7] kernel: Add support for restart notifier call chain |
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On 07/07/2014 02:14 PM, Andrew Morton wrote: > On Sun, 6 Jul 2014 16:38:14 -0700 Guenter Roeck <linux@roeck-us.net> wrote: > >> Various drivers implement architecture and/or device specific means >> to restart (reset) the system. Various mechanisms have been implemented >> to support those schemes. The best known mechanism is arm_pm_restart, >> which is a function pointer to be set either from platform specific code >> or from drivers. Another mechanism is to use hardware watchdogs to issue >> a reset; this mechanism is used if there is no other method available >> to reset a board or system. Two examples are alim7101_wdt, which currently >> uses the reboot notifier to trigger a reset, and moxart_wdt, which registers >> the arm_pm_restart function. >> >> The existing mechanisms have a number of drawbacks. Typically only one scheme >> to restart the system is supported (at least if arm_pm_restart is used). >> At least in theory there can be mutliple means to restart the system, some of >> which may be less desirable (for example one mechanism may only reset the CPU, >> while another may reset the entire system). Using arm_pm_restart can also be >> racy if the function pointer is set from a driver, as the driver may be in >> the process of being unloaded when arm_pm_restart is called. >> Using the reboot notifier is always racy, as it is unknown if and when >> other functions using the reboot notifier have completed execution >> by the time the watchdog fires. >> >> To solve the problem, introduce a system restart notifier. This notifier >> is expected to be called from the architecture specific machine_restart() >> function. Drivers providing system restart functionality (such as the watchdog >> drivers mentioned above) are expected to register with this notifier. > > It all looks sane to my unfamiliar eye. > >> /* >> + * Notifier list for kernel code which wants to be called >> + * to restart the system. >> + */ > > hm, is this all we have to say? > >> --- a/kernel/reboot.c >> +++ b/kernel/reboot.c >> @@ -104,6 +104,38 @@ int unregister_reboot_notifier(struct notifier_block *nb) >> } >> EXPORT_SYMBOL(unregister_reboot_notifier); >> >> +/** >> + * register_restart_notifier - Register function to be called to reset >> + * the system >> + * @nb: Info about notifier function to be called >> + * >> + * Registers a function with the list of functions >> + * to be called to restart the system. >> + * >> + * Currently always returns zero, as blocking_notifier_chain_register() >> + * always returns zero. >> + */ > > This would be a good place to describe what those notifier callbacks > actually do. Why they exist, what their role is, under what > circumstances they are called, what values they should return, etc. >
Makes sense. Done.
Guenter
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